1. Field of the Invention
The present invention relates to a device and method for pumping fluids, and more particularly, to a device and method for pumping fluids employing the movement of gas bubbles through channels in microscale.
2. Description of the Related Art
A micro-fluidic system refers to a system combining fluid dynamics and Micro-Electro-Mechanical Systems (MEMS), which can control fluid flows in micro units. For example, systems are being developed to perform tasks such as extracting DNA from very small test samples, checking gene mutation, and so on.
Pumping fluids such as bio-fluids and chemical solutions through microscale channels is closely related to future micro-fluidic systems such as lab-on-a-chip (LOC) or micro total analysis systems (μTAS).
U.S. Pat. No. 6,071,081 discloses a heat-powered liquid pump applying a film-boiling phenomenon. The pump is constructed with a chamber having inlet and outlet valves and a heating system located on the bottom surface of the chamber. The liquid is heated in the chamber by the heating system to form bubbles. The bubbles repeatedly expand and contract due to heat energy pulses. The bubbles act as a pressure source to expel liquid out of the chamber during bubble expansion and to draw liquid into the chamber during bubble contraction. Such a method can separate and transport liquid. The delivery volume of the pump depends on the bubble size and numbers.
The above method has a disadvantage of degrading reliability where the pump runs for an extended time since small actuating values employed for net fluid movements, and preventing reverse flows, are delicate parts that have to be very carefully manufactured. Delicate parts like those can be damaged during extended pump running times.
The paper of J. H. Tsai and L. Lin on “A thermal-Bubble-Actuated Micronozzle-Diffuser Pump” published on J. Microelectromechanical Systems, Vol. 11, No. 6, pp. 665-667 in 2003 addresses a mechanism for periodically re-forming and collapsing thermal bubbles. The micro pump has a resistance heater, a pair of nozzle-diffusing flow controllers, and a pumping chamber. Net flows are produced from the nozzles to the diffuser. This micro pump has some disadvantages such as particles possibly blocking the nozzle diffusion paths and damage to the pumping chamber due to bubble-collapsing pulses.
U.S. Pat. No. 6,283,718 discloses a method of pumping liquid through channels. The liquid is disposed within a liquid chamber or channel. Power is applied to a micro pump to form vapor bubbles in the chamber or channel. Through a formation and collapsing cycle of the vapor bubbles, a pumping action of the liquid is effectuated.
The paper of Song and Zhao on “Modeling and test of thermally-driven phase change non-mechanical pump” published on J. Micormech. Microeng, Vol. 11, pp. 713-719 in 2001 discloses a non-mechanical micro-pump driven by phase change. The pump has a glass tube and a few thermal elements distributed uniformly. Through control of the thermal elements along the glass tube, a pumping action is created. That is, changing the location where power is applied to heat sources produces the movement of vapor bubbles, which results in the pumping of liquid.
The above pump requires a high power consumption of more than 10 Watts, features slow thermal responses, and requires manual control of phase growth.
One severe disadvantage of the aforementioned pumping principles and pumps is that heating the pumped fluids to its boiling point can not be applied to most pumped fluids and corresponding micro-fluidic devices.
The paper of N. R. Tas, T. W. Berenschot, T. S. J. Lammerink, M. Elwenspoek, A. Van den Berg on “Nanofluidic Bubble Pump Using Surface Tension Directed Gas Injection” published on Anal. Chem. Vol. 74, pp. 2224-2227 in 2002 addresses a method of manipulating liquid with a hydrophilic fluid channel having a minutely machined surface. The method is based on surface tension-directed gas injection through minute-sized holes in the channel walls. The injected gas is discharged by asymmetrically cross-sectioned surfaces of the micro channels, by which an infinitesimal quantity of liquid is transported.
The drawback to this micro pump goes to specific structures of a manual pressure-applying mechanism and micro channels. Other disadvantages of such a pumping principle include a complicated manufacturing process and conductive heat loss. The inaccurate control on bubble transportation through channels and heaters requires a certain countermeasure on temperature control and packaging.